In the related art, there is a known artificial lung having a hollow fiber membrane bundle which is configured with multiple hollow fiber membranes (for example, U.S. Pat. No. 4,911,846). U.S. Pat. No. 4,911,846 discloses a hollow fiber membrane bundle having a bamboo blind shape in which multiple hollow fiber membranes are disposed substantially in parallel so as to serve as the weft and the weft is interwoven with the warp. A hollow fiber sheet having such a bamboo blind shape is folded such that the hollow fiber membrane bundle can have a prismatic shape or a columnar shape as the outer shape.
In the hollow fiber membrane bundle having such a configuration, there is concern that gas exchange or heat exchange may be insufficient in a portion where the weft (hollow fiber membranes) and the warp (warp threads) overlap each other. In addition, there is concern that blood is likely to stay and a thrombus may be formed in the portion where the weft and the warp overlap each other.
In order to solve the foregoing problems, it is preferable that the hollow fiber membranes are wound manyfold on the outer periphery of a round rod body, for example, around a central axis thereof so as to be a hollow fiber membrane bundle having a cylindrical body shape.
However, as the number of times of winding the hollow fiber membranes increases, the total volume of gaps between the hollow fiber membranes increases. As a result thereof, the amount of blood passing through the gaps, that is, the blood filling amount also increases. Accordingly, a burden to a patient (i.e., the priming volume of the membrane bundle) becomes significant.
Therefore, it is possible to consider using a hollow fiber membrane having a small outer diameter. Accordingly, while the surface area of the hollow fiber membrane which comes into contact with blood is maintained, the total volume of the gaps between the hollow fiber membranes can be prevented from increasing and the blood filling amount can be reduced.
However, when the outer diameter of the hollow fiber membrane is reduced, the inner diameter is also reduced. Therefore, a pressure loss of a fluid pas sing through the inside of the hollow fiber membrane increases. If the pressure loss of a fluid increases, for example, in a case of an artificial lung section, there is concern that gas may flow out from the hollow fiber membrane to the outside.